<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    h1 {
      color: black;
    }
    h1::after {
      content: '手机';
    }
    @media screen and (min-width: 768px) and (max-width: 992px) {
      h1 {
        color: red;
      }
      h1::after {
        content: '平板';
      }
    }
    @media screen and (min-width: 992px) and (max-width: 1200px) {
      h1 {
        color: blue;
      }
      h1::after {
        content: '小型笔记本';
      }
    }

    @media screen and (min-width: 1200px) {
      h1 {
        color: green;
      }
      h1::after {
        content: '液晶屏幕';
      }
    }
  </style>
</head>
<body>
  <h1>当前屏幕：</h1>
</body>
</html>